tmpfs: disallow CONFIG_TMPFS_INODE64 on s390

Currently there is an assumption in tmpfs that 64-bit architectures also
have a 64-bit ino_t.  This is not true on s390 which has a 32-bit ino_t.
With CONFIG_TMPFS_INODE64=y tmpfs mounts will get 64-bit inode numbers
and display "inode64" in the mount options, but passing the "inode64"
mount option will fail.  This leads to the following behavior:

  # mkdir mnt
  # mount -t tmpfs nodev mnt
  # mount -o remount,rw mnt
  mount: /home/ubuntu/mnt: mount point not mounted or bad option.

As mount sees "inode64" in the mount options and thus passes it in the
options for the remount.

So prevent CONFIG_TMPFS_INODE64 from being selected on s390.

Link: https://lkml.kernel.org/r/20210205230620.518245-1-seth.forshee@canonical.com
Fixes: ea3271f7 ("tmpfs: support 64-bit inums per-sb")
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Hugh Dickins <hughd@google.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: <stable@vger.kernel.org>	[5.9+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/Kconfig

@@ -203,7 +203,7 @@ config TMPFS_XATTR
 
 config TMPFS_INODE64
 	bool "Use 64-bit ino_t by default in tmpfs"
-	depends on TMPFS && 64BIT
+	depends on TMPFS && 64BIT && !S390
 	default n
 	help
 	  tmpfs has historically used only inode numbers as wide as an unsigned